The 28-hour countdown for the launch of ISRO's 100th satellite along with 30 others in a single mission, from the space port of Sriharikota, about 110 kms from here, began today.

On its 42nd mission, the Indian Space Research Organisation's (ISRO) trusted workhorse 'PSLV-C40' will carry the weather observation 'Cartosat-2' series satellite and 30 co-passengers (together weighing about 613 kg) at lift-off at 9.28 am tomorrow.

The co-passenger satellites comprise one micro and nano satellite each from India as well as three micro and 25 nanosatellites from six countries -- Canada, Finland, France, Korea, the United Kingdom and United States of America.

The total weight of all the 31 satellites carried on-board PSLV-C40 is about 1,323 kgs.

The 28 international customer satellites are being launched as part of the commercial arrangements between ISRO and its commercial arm 'Antrix Corporation Ltd'.

Of the total number of satellites carried by PSLV-C40, 30 satellites will be launched into a 505 kms polar Sun Synchronous Orbit (SSO).

Scientists would bring down the height by twice restarting the fourth stage of the PSLV-C40 for launch of Microsat satellite, which will be placed in a 359 kms polar SSO, ISRO said.

The entire launch of satellites is expected to happen over a period of 2 hours and 21 seconds, it said.

According to ISRO, the Cartosat-2 series satellite launch is a follow-on mission with the primary objective of providing high resolution scene specific spot imageries.

It carries panchromatic and multi-spectral cameras operating in Time Delay Integration mode and is capable of delivering high resolution data.

It will be the third satellite in the Cartosat-2 series.

ISRO had successfully launched Cartosat-2 Series satellite on June 22, 2016.

It is similar to the earlier Cartosat-2, 2A and 2B.

The images sent by Cartosat-2 series satellite will be useful for cartographic applications, urban and rural applications, coastal land use and regulation, road network monitoring, water distribution, creation of land use maps and change detection to bring out geographical Land Information Systems and Geographical Information System applications.

Tomorrow's launch also marks the first launch for ISRO in 2018 following the unsuccessful mission of navigation satellite IRNSS-1H last year.

On August 31, 2017 India's mission to launch its backup navigation satellite IRNSS-1H on board PSLV-C39 failed after the heat shield did not separate in the final leg of the launch sequence and as a result, the satellite IRNSS-1H got stuck in the fourth stage of the rocket.

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